Hydrolysis-resistant polyamide molding materials for use in gas injection techniques (git)

ABSTRACT

The present invention provides a composition of reinforced polyamide (PA) for use in a cooling circuit of an engine. The composition may be processed by a gas injection technique (GIT) into shaped parts having smooth inner surfaces and a good hydrolytic stability against cooling medium such as glycol/water mixtures.

[0001] This invention relates to compositions of reinforced PA for usein the coolant circuit, which compositions, when processed using theGAIM process, give rise to mouldings with smooth internal surfaces andgood hydrolysis resistance towards coolant (glycol/water mixtures).

[0002] Glass-reinforced polyamides, in particular polyamide 66 (PA66),generally reinforced with 30 to 35 wt. % of glass fibre, have been usedsuccessfully for injection moulded automotive coolant circuit mouldingsfor years. Typical applications are the radiator tank and coolantmanifold. Such mouldings exhibit adequate resistance to the coolant (inmost cases 1:1 ethylene glycol/water mixtures), even at temperatures ashigh as 130° C.

[0003] In addition to the stated applications, it would be desirable forreasons of more favourable production costs and greater reliability inservice and durability/corrosion resistance, to replace the metal tubesand rubber hoses in the coolant circuit entirely or in part withthermoplastic tubes. Reinforced PA66 should preferably be used for thisapplication too since, from the standpoint of low-cost production, it atpresent provides the best compromise between the greatest possiblehydrolysis resistance and low material costs. However, when producingtubes by injection moulding, restrictions apply with regard to thepossible geometries. Curved tubes cannot be produced using standardinjection moulding. While there are indeed specific processes forproducing hollow articles with curved internal surfaces (for examplefusible core process), these are associated with elevated additionalcosts.

[0004] One low cost alternative could be injection moulding by the GAITprocess (GAIT=gas-assisted injection moulding), but this usually resultsin very rough internal surfaces which, due to their elevated surfacearea, are more susceptible to attack by the coolant flowing over them.Moreover, there is an increased risk of detachment of glass fibres fromthe surface, which may then possibly circulate in the coolant circuitand have an abrasive action or form partial deposits or even blockages.While completely dispensing with glass fibres results in smootherinternal surfaces, the mechanical properties of the mouldings are thenno longer adequate (excessively low modulus of elasticity, excessivelylow strength) and hydrolysis resistance is greatly reduced. Somewhatbetter hydrolysis resistance may be achieved by combining glassfibres/glass beads, but the overall level of properties of suchcompounds is inadequate. Similar considerations apply to compounds whichhave exclusively mineral reinforcement.

[0005] The object of the invention was to provide a material and aprocess which makes it possible to produce mouldings with a smoothinternal surface and good hydrolysis resistance towards coolant(glycol/water mixtures) by the gas-assisted injection moulding process(GAIM process).

[0006] It has surprisingly now been found that the combination of glassfibres with mica, in particular with phlogopite mica, in the PA66compound gives rises to materials which, with conventional addition ofadditives, are not only suitable for producing tubes by the gas-assistedinjection moulding process, but also give rise to finished parts with arelatively smooth internal surface and very good hydrolysis resistance.Particularly good finished part quality with regard to a smooth internalsurface and uniform wall thickness distribution has been achieved by thefollowing adaptations to the generally described (in Kunststoffe 1990,8068, 873-876, Carl Hanser Verlag Munich, 1990) gas-assisted injectionmoulding (GAIM) process or by selection of the following conditionsduring GAIM processing:

[0007] expulsion process

[0008] gas injection via heatable annular slit gas injector with reducedmelt in the gas outlet zone

[0009] use of a labyrinth seal to provide a seal between the melt andgas injector

[0010] gas inlet upstream from the melt gate (relative to main directionof melt flow)

[0011] control of wall thickness of finished part by velocity of gasbubble front

[0012] use of overflow cavities and associated overflow channels, thevolume of which is adjustable.

[0013] The present invention provides thermoplastic mouldingcompositions consisting of 40 to 80 parts by weight of polyamide,preferably PA66, 0 to 45 parts by weight, preferably 5 to 45 parts byweight of glass fibres or other fibrous reinforcing materials, 5 to 45parts by weight of mica or other lamellar mineral reinforcing materialsor fillers and 0 to 5 parts by weight of other additives, such as forexample conventional stabilising and processing auxiliaries and dyes,wherein the sum of all the weight percentages must be 100.

[0014] Suitable polyamides are known homopolyamides, copolyamides andmixtures of these polyamides. Said polyamides may be partiallycrystalline and/or amorphous.

[0015] Suitable partially crystalline polyamides are polyamide 66,polyamide 6, mixtures and corresponding copolymers prepared from thesecomponents. Further polyamides which may be considered are those, theacid component of which consists entirely or in part of terephthalicacid and/or isophthalic acid and/or suberic acid and/or sebacic acidand/or azelaic acid and/or adipic acid and/or cyclohexanedicarboxylicacid, the diamine component of which consists entirely or in part of m-and/or p-xylylenediamine and/or hexamethylenediamine and/or2,2,4-trimethylhexamethylenediamine and/or2,2,4-trimethylhexamethylenediamine and/or isophoronediamine and thecomposition of which is known in principle.

[0016] Further polyamides which may be mentioned are those which areproduced entirely or in part from lactams having 7 to 12 C atoms,optionally together with one or more of the above-stated startingcomponents.

[0017] Polyamide 6,6 is particularly preferred.

[0018] Copolymers which are obtained by polycondensation of two or moremonomers are also suitable, as are copolymers which are produced withthe addition of aminocarboxylic acids, such as -aminocaproic acid,-aminoundecanoic acid or -aminolauric acid or the lactams thereof.

[0019] The polyamides preferably exhibit a relative viscosity (measuredon a 1 wt. % solution in m-cresol at 25° C.) of 2.7 to 3.5.

[0020] The moulding compositions according to the invention may containadditives such as colorants, stabilisers (in particular stabiliserscontaining copper), lubricants and processing auxiliaries, optionallytogether with further additives.

[0021] The polyamides may additionally contain further fibrousreinforcing materials and/or mineral fillers. Fibrous reinforcingmaterials other than glass fibres which may be considered are carbonfibres, aramid fibres, mineral fibres and whiskers. Suitable mineralfillers which may be mentioned by way of example are calcium carbonate,dolomite, calcium sulfate, mica, fluorine mica, wollastonite, talcum andkaolin. It is, however, also possible to use other oxides or hydratedoxides of an element selected from the group boron, aluminium, gallium,indium, silicon, tin, titanium, zirconium, zinc, yttrium or iron. Thefibrous reinforcing materials and the mineral fillers may be surfacetreated to improve mechanical properties.

[0022] Glass fibres are preferred.

[0023] Reinforcing materials which may be considered in addition to orinstead of glass fibres are also carbon fibres, aramid fibres, mineralfillers or reinforcing materials and similar materials. These mayoptionally be provided with surface modifications, for example silanesor glass fibre sizes.

[0024] The present invention furthermore provides moulding compositionsaccording to the invention which additionally contain 0.01 to 10 partsby weight, particularly preferably 0.3 to 1.0 parts by weight ofantinucleating (crystallisation inhibiting) additives, wherein the sumof all parts by weight must be 100.

[0025] The present invention provides moulding compositions in which thelamellar reinforcing material is phlogopite mica.

[0026] The present invention also provides the use of the mouldingcompositions according to the invention for the production of mouldingsfor the automotive coolant circuit.

[0027] The present invention also provides the use of the mouldingcompositions according to the invention for the production of mouldingsfor the automotive coolant circuit by means of a gas-assisted injectionmoulding process.

[0028] The present invention also provides the use of the mouldingcompositions according to the invention for the production of mouldingsfor the automotive coolant circuit by means of a gas-assisted injectionmoulding process, wherein the melt expulsion method is preferably used.

[0029] The present invention also provides the use of the mouldingcompositions according to the invention for the production of mouldingsfor the automotive coolant circuit by means of a gas-assisted injectionmoulding process, wherein the standard GAIM process (melt inflationmethod) or the melt expulsion method or a combination of inflation andexpulsion methods is preferably used.

[0030] The present invention also provides a process for the productionof mouldings using the GAIM process, characterised in that the followingare combined

[0031] expulsion process

[0032] gas injection via heatable annular slit gas injector with reducedmelt in the gas outlet zone

[0033] use of a labyrinth seal to provide a seal between the melt andgas injector

[0034] gas inlet upstream from the melt gate (relative to main directionof melt flow)

[0035] control of wall thickness of finished part by velocity of gasbubble front

[0036] use of overflow cavities and associated overflow channels, thevolume of which is adjustable.

[0037] The present invention also provides mouldings produced accordingto one or more of the preceding claims.

EXAMPLE

[0038] GAIM Processing

[0039] S-shaped automotive coolant tubes (total length 250 mm, externaldiameter 19 mm, average wall thickness 3 mm) with a connector wereproduced from the various materials listed in Example 1 using thegas-assisted injection moulding process (expulsion method). Theinjection moulding machine used was an Engel ES 700/150. Gas wasinjected via an annular slit gas injector with adjustable annular slitwidth and integral labyrinth seal. Melt temperatures were adjusted, inaccordance with the moulding composition standard relevant to thematerials, to between 280 and 310° C., while the mould temperature wasapprox. 80° C. for all tests. Gas was injected at pressures of 100 to300 bar, in most cases at approx. 250 bar. The pressure gas wasnitrogen, which was apportioned by a Battenfeld Airmold unit.

[0040] Production of Compounds

[0041] The polyamide compounds used in Examples 1 to 4 and 11 andComparative Example 12 and 13 were produced by compounding polyamide 66or polyamide 6 with the reinforcing materials and additives listed inTable 1 in Werner & Pfleiderer ZSK 32 twin screw extruders in theconventional manner (melting of the polymer, optionally as a mixturewith the additives, addition of the reinforcing materials to thepolyamide melt, drawing off the strand through a water bath andsubsequent pelletisation). Before further processing, the resultantpellets were dried to a residual moisture content of <0.12% at 70° C.under a vacuum.

[0042] In Examples 5 to 10, mineral-filled compounds were physicallymixed in pellet form with glass fibre-reinforced PA66 (Durethan AKV 30HR H2.0 9005/0, commercial product of Bayer AG) in various ratios andfurther processed in this form (as a “dry blend”).

[0043] Determination of Mechanical Properties When Freshly InjectionMoulded and After Immersion in Coolant

[0044] The values for mechanical properties stated in the Table weredetermined on standard 80×10×4 mm test specimens, which were produced inaccordance with the relevant moulding composition standards. Izod impactstrength was determined to ISO 180 1C, while flexural modulus wasdetermined in accordance with the ISO 178 flexural test.

[0045] The influence of coolant on mechanical properties wasinvestigated by immersing unnotched standard 80×10×4 mm test specimensin an autoclave at 130° C. filled with coolant (1 L ethylene glycol/1 Lwater). A pressure of approx. 2 bar is established in this manner. After42 days' immersion under these conditions, after cooling to roomtemperature, the test specimens were removed, rinsed with water, driedand heat-sealed in PE film. After 4 hours' equalisation, testing wasperformed. Glass Glass Phlogopite PA6 PA66 microbeads¹⁾ fibres² mica³⁾Kaolin⁵⁾ Talc⁶⁾ Composition⁴⁾ [%] [%] [%] [%] [%] [% ] [%] ComparativeExample 1 67.6 20 10 — Example 2 67.6 10 20 Example 3 57.6 10 30 Example4 57.6 40 Example 5⁷⁾ 43.2 22.6 10 20 Example 6⁸⁾ 48.6 16.9 7.5 22.5Example 7⁹⁾ 27.7 38.2 12.3 17.7 Example 8¹⁰ 63.7 10 20 Example 9¹¹⁾ 59.47.5 22.5 Example 10¹²⁾ 61.1 12.3 17.7 Example 11 64.8 10 20 ComparativeExample 12 99.5 Comparative Example 13 67.6 30

[0046] 1) CP 3000, commercial product of Potters Ballotini

[0047] 2) Vetrotex P 955, commercial product of Vetrotex

[0048] 3) e.g. Kemira Mica 100S of Kemira or Mica 5100 S, commercialproduct of Polar Minerals

[0049] 4) All compounds contain copper iodide (300-400 ppm) mixed withpotassium bromide (800 to 1000 ppm) as heat stabiliser, approx. 0.2%demoulding auxiliary (amide wax or montan ester wax), 0.2 to 0.8%blackening agent (carbon black, nigrosine) and approx. 200 ppm microtalcas nucleating agent

[0050] 5) Polarite 102 A from Imerys

[0051] 6) Naintsch A 60, commercial product of Talc de Luzenac

[0052] 7) Mixture of 33.3% PA66 GF30 (Durethan AKV 30 HR H2.0 9005/0,commercial product of Bayer AG) with 66.7% Durethan BM 230 H2.0 9005/0(commercial product of Bayer AG)

[0053] 8) 25% Durethan AKV 30HR H2.0 9005/0 (commercial product of BayerAG) 75% Durethan BM 230 H2.0 9005/0 (commercial product of Bayer AG)

[0054] 9) 41% Durethan AKV 30 HR H2.0 9005/0 (commercial product ofBayer AG) 59% Durethan BM 230 H2.0 9005/0 (commercial product of BayerAG)

[0055] 10) 33.3% Durethan AKV 30 HR H2.0 9005/0 (commercial product ofBayer AG) 66.7% Durethan AM 140 H2.0 9005/0 (commercial product of BayerAG)

[0056] 11) 25% Durethan AKV 30 HR H2.0 9005/0 (commercial product ofBayer AG) 75% Durethan AM 140 H2.0 9005/0 (commercial product of BayerAG)

[0057] 12) 41% Durethan AKV 30 HR H2.0 9005/0 (commercial product ofBayer AG) 59% Durethan AM 140 H2.0 9005/0 (commercial product of BayerAG) Ra Average Wt roughness Maximum Izod impact Izod impact Flexuralvalue of wave depth strength, strength after Flexural modulus afterRoughness of internal of internal freshly 42 days^(\) modulus, freshly42 days′ internal surface surface injection imersion injection immersionin surface of of tube of tube moulded in coolant moulded coolant tube[μm] [μm] [kJ/m²] [kJ/m²] [MPa] [MPa] Comparative Example smooth 29 65800 1230 1 Example 2 smooth-rough 6.9 80.3 37 10 8120 2200 Example 3smooth-rough 9.6 130.0 28 7 10900 2070 Example 4 smooth 1.3 18.3 17 911400 2910 Example 5⁷⁾ smooth 5.6 72.1 44 6100 Example 6⁸⁾ smooth 3.749.7 47 5730 Example 7⁹⁾ smooth-rough 4.4 76.9 45 6160 Example 8¹⁰⁾smooth 5.4 86.9 29 9 9540 2950 Example 9¹¹⁾ smooth 6.4 67.1 26 8 96202800 Example 10¹²⁾ smooth 4.6 57.6 35 10 9350 3030 Example 11 smooth 376 5640 1430 Comparative Example smooth <1 <10 140 <1 3200 <100 12Comparative Example very rough 11.5 165 65 8 8590 3100 13

1. Thermoplastic moulding compositions consisting of 40 to 80 parts byweight of polyamide, 0 to 45 parts by weight, preferably 5 to 45 partsby weight of glass fibres or other fibrous reinforcing materials, 5 to45 parts by weight of mica or other lamellar mineral reinforcingmaterials or fillers and 0 to 5 parts by weight of additives, whereinthe sum of all the weight percentages must be
 100. 2. Mouldingcompositions according to claim 1, which additionally contain 0.01 to 10parts by weight of antinucleating additives, wherein the sum of all theweight percentages must be
 100. 3. Moulding compositions according toclaim 1 and/or 2, in which the lamellar reinforcing material isphlogopite mica.
 4. Use of the moulding compositions according to one ormore of the preceding claims for the production of mouldings for theautomotive coolant circuit.
 5. Use of the moulding compositionsaccording to one or more of the preceding claims for the production ofmouldings for the automotive coolant circuit by means of a gas-assistedinjection moulding process.
 6. Use of the moulding compositionsaccording to one or more of the preceding claims for the production ofmouldings for the automotive coolant circuit by means of a gas-assistedinjection moulding process, wherein the standard GAIM process (meltinflation method) or the melt expulsion method or a combination ofinflation and expulsion methods is used.
 7. A process for the productionof mouldings using the GAIM process, characterised in that the followingare combined expulsion process gas injection via heatable annular slitgas injector with reduced melt in the gas outlet zone use of a labyrinthseal to provide a seal between the melt and gas injector gas inletupstream from the melt gate (relative to main direction of melt flow)control of wall thickness of finished part by velocity of gas bubblefront use of overflow cavities and associated overflow channels, thevolume of which is adjustable.
 8. Mouldings produced according to one ormore of the preceding claims.